Probiotics are microbial-based dietary adjuvants that beneficially affect the host physiology by modulating mucosal and systemic immunity, as well as improving nutritional and microbial balance in the intestinal tract [Naidu A S, Bidlack W R, Clemens R A (1999) Probiotic spectra of lactic acid bacteria (LAB). Crit. Rev. Food Sci. Nutr. 39:3–126]. Lactic acid bacteria (LAB) are indigenous probiotic microflora of mammalian gastrointestinal tract that play an important role in the host microecology and have been credited with an impressive list of therapeutic and prophylactic properties [Naidu A S, Clemens R A (2000) Probiotics, p.431–462. In A. S. Naidu (ed.), Natural Food Antimicrobial Systems. CRC Press, Boca Raton, Fla.]. These therapeutic and prophylactic properties include, but not limited to the maintenance of microbial ecology of the gut, physiological, immuno-modulatory and antimicrobial effects [Gibson G R, Saavedra J M, Macfarlane S, Macfarlane G T (1997) Probiotics and intestinal infections, p.10–39. In R. Fuller (ed.), Probiotics 2: Applications and practical aspects. Chapman and Hall, London, UK]. Other LAB associated attributes include enzyme release into the intestinal lumen that act synergistic with LAB adhesion to alleviate symptoms of intestinal malabsorption. Furthermore, the LAB-released enzymes help regulate intestinal pH that results in increased aromatic amino acid degradation [Mitsuoka T (1984) Taxonomy and ecology of bifidobacteria. Bifidobacteria Microflora 3:11]. LAB have also demonstrated the ability to significantly reduce sulfide and ammonia containing compounds in animal fecal waste and thus reduce the odor and toxicity associated with animal excrements [Naidu A S, Xie X, Leumer D A, Harrison S, Burrill M J, Fonda E A (2002) Reduction of sulfide, ammonia compounds and adhesion properties of Lactobacillus casei strain KE99 in vitro. Curr. Microbiol. 44:196–205].
However, the greatest potential for LAB to improve life quality for man and domestic animals lies in their in vivo probiotic applications. In order for LAB to exhibit beneficial probiotic effects in vivo, the organisms must survive for extended time periods in the gut. Therefore, it is critical that probiotic LAB strains be selected that possess qualities that prevent their rapid removal by gut contraction [Havenaar R, Brink B, Huis in't Veld JHJ (1992) Selection of strains for probiotic use, p.209–224. In R. Fuller (ed.), Probiotics, the scientific basis. Chapman and Hall, London, UK]. Effective probiotic bacteria should be able to survive gastric conditions and colonize the intestine, at least temporarily, by adhering to the intestinal epithelia [Conway P (1996) Selection criteria for probiotic microorganisms. Asia Pacific J. Clin. Nutr 5:10–14].
Furthermore, in addition to increasing in vivo viability and gastrointestinal tract life span, prolonged shelf life at room temperature remains a commercial challenge. Lactic acid bacilli generally require an effective delivery system that retains probio-functional activities (i.e. gut adhesion/retention, production of bacteriocins/enzymes) after their revival [Salminen S, Isolauri E, Salminen E (1996) Clinical uses of probiotics for stabilizing the gut mucosal barrier: successful strains and future challenges. Antonie Van Leeuwenhoek 70:347–3581.] Though freeze-drying is an effective process for preservation and delivery of probiotics, several physico-chemical factors such as humidity, aeration (oxygen availability) and temperature could compromise the cell viability, thereby the shelf life.
One potential additive class that may increase both in vivo life span and storage shelf-life is prebiotics. Prebiotics are non-digestible, or partially digestible, food ingredients that beneficially affect the host by selectively simulating the growth and/or activity of one or a limited number of bacterial species and thus in effect improve host health. [Gibson G R, Roberfroid M B (1995) Dietary modulation of the human colonic microbiota: Introducing the concept of prebiotics. J. Nutr. 125:1401–1412]. Intake of prebiotics can beneficially modulate probiotic LAB. Non-digestible oligosaccharides such as dietary fiber in general, and fructo-oligosaccharides (FOS) in particular, are well known prebiotics [Roberfroid M B (1997) Health benefits of non-digestible oligosaccharides. Adv. Exp. Med. Biol. 427:211–219]. By combining the rationale of probiotics and prebiotics, the concept of ‘synbiotics’ is proposed to characterize some colonic foods with interesting nutritional properties in combination with health-enhancing functional food ingredients [Fuller R, Gibson G R (1997) Modification of the intestinal microflora using probiotics and prebiotics. Scand. J. Gastroenterol. Suppl. 222:28–31].
Essential oils are known as biological preservatives due to their low water activity and limited air diffusion. Several essential oils also known to provide various nutraceutical benefits including antioxidant, antimicrobial, antitumor, and immune-modulatory activities. However, the prebiotic effects of essential oils on probiotic LAB are heretofore unknown. Therefore, there remains a need to enhance probiotic activity, in vivo viability and shelf life of probiotic compositions including LAB. One potential solution is the application of prebiotics in combination with advanced packaging methods.